The present invention relates to the synthesis of 3-amino-1,2,4-triazole, and more particularly, it relates to a method for synthesizing this aminotriazole in a purer form and with improved yields.
3-Amino-1,2,4-triazole has the formula: ##STR1## and is employed chiefly as weedkiller and, to a lesser extent, as a starting material for chemical syntheses (more particularly in the dye industry).
Commercially, 3-amino-1,2,4-triazole is obtained by reacting an aminoguanidine salt (usually the bicarbonate) with formic acid, followed by cyclization of the aminoguanidine formate so produced, as shown in U.S. Pat. No. 2,875,209. In the initial stage, the aminoguanidine is obtained in the form of a water-soluble salt by condensation of hydrazine hydrate with cyanamide in the presence of an inorganic acid, usually sulfuric acid, and isolated in the form of a poorly soluble bicarbonate by carbonation in an alkaline medium, as shown in French Pat. No. 1,241,151.
This prior art commercial process, however, has major disadvantages. The economics are adversely affected by a number of factors. First, a large excess of cyanamide is required to obtain complete conversion of the hydrazine hydrate; an inorganic acid is used and this accordingly requires an alkaline agent in the carbonation stage. Further, it entails consumption of carbon dioxide; loses yield due to partial solubility of the aminoguanidine bicarbonate in the mother liquors and washes, recycling of which is impossible, particularly because of the presence of inorganic ions; and occasions a large volume of heavy polluting effluents which it is impossible to purify to an acceptable level.
Additionally, 3-amino-1,2,4-triazole from this prior art process is insufficiently pure. The aqueous solutions are not easily filterable, an indication of the presence of insoluble products which, while present in small amounts, are all the more difficult because in most cases they are in the form of a gel.
Published Japanese patent application No. 72/08,820 suggests preparing 3-amino-1,2,4-triazole by the reaction of hydrazine hydrate with cyanamide in the presence of formic acid, this operation being carried out in a single stage (Examples 1 to 9) or in two stages (Example 10). In both cases, the purity of the 3-amino-1,2,4-triazole produced is unsatisfactory, because the aqueous solutions develop more or less gelatinous flocculates, which are difficult to remove. Furthermore, the yield obtained by operating as in Example 10 is too low to make this process economically viable.